The present invention relates to an apparatus for measuring the infrared spectrum of microfine portions and, more particularly, to an infrared spectrum measuring microscope apparatus which is suitable for accurately identifying the material at a microfine portion.
An infrared spectrum measuring apparatus generally known is composed of an infrared source, a monochrometer for obtaining the infrared intensity for each wavelength component or an interferometer, an infrared detector, a sample chamber, etc. The measurement of the infrared spectrum of a microfine portion is conventionally carried out by a Fourier infrared spectrometer using an interferometer, which has a high sensitivity, in combination with a microscope apparatus such as those discussed by Robart G Messershmidt on pp. 27 to 31 of "The Design, Sample Handling and Application of Infrared Microscopes, ASTM STD 949, American Society for Testing and Materials", Philadelphia (1987)" and on pp. 85 to 87 of "Practical Spectroscopy Series Volume 6, Infrared Microspectroscopy, edited by Robart G Messershmidt", MARCEL DEKKER INC. (1988).
These papers contain the schematic views of a microscope such as those shown in FIGS. 14 and 15. The reference numeral 1 in FIGS. 14 and 15 represents sample stages, 2 and 3 in FIG. 14 and 2 in FIG. 15 represent reflecting objectives, 3 in FIG. 15 represents an ellipsoidal converging mirror for illuminating a sample, 4, 4' in FIG. 14 and 4, in FIG. 15 represent apertures for regulating the measuring visual field, 5 in FIG. 15 a reflecting objective for converging light, and 6 in FIGS. 14 and 15 represents an infrared detector Infrared rays from a Fourier transform infrared spectrometer are represented by the reference numeral 5 in FIG. 14 and 7 in FIG. 15. The infrared spectrum of a sample is generally measured either in a transmission mode or reflection mode. Infrared rays from a Fourier transform infrared spectrometer of a transmission measuring mode are represented by the reference numeral 7 in FIGS. 14 and 15, and infrared rays for measurement in a reflection mode are represented by the reference numeral 5 in FIG. 14, but not shown in FIG. 15. It is assumed to be because infrared rays are projected to the reflecting objective 2 in FIG. 15 through an ellipsoidal mirror 8 in FIG. 15, but details are not described. In this way, since a conventional apparatus utilizes the optical system of an ordinarily used optical microscope, no consideration is given to the size or the like of the object of measurement. That is, since the downward movement of the sample stage 1 in FIG. 15 is restricted by the converging mirror 3 for converging infrared on the sample, and the upward movement of the sample stage 1 is restricted by the reflecting objective 2, the size of the sample to be placed on the sample stage 1 is disadvantageously restricted. In the case of spectral measurement in a transmission mode, the measurable thickness of a sample is 10 to 20 .mu.m by infrared spectral measurement and several cm in an ordinary spectral measurement of a visible region. In this way, spectral measurement in a transmission mode is naturally not intended for a large sample. On the other hand, in the case of spectral measurement in a reflection mode, the surface of a sample is the object of measurement. The conventional apparatus having a limitation in the vertical movement of the sample stage is therefore disadvantageous in that some large samples cannot be placed on the sample stage. This problem produces another serious defect when various jigs for spectral measurement are used in this apparatus.
The problem of the limitation in the vertical movement of the sample stage is produced because neither the converging mirror 3 in FIG. 15 for converging infrared rays on a sample can be lowered in the optical path of infrared rays nor can the reflecting objective 2 be lifted. In addition, measurement of an infrared spectrum or the like is strongly influenced by vapor, carbon dioxide gas, etc. in air. It is therefore necessary to minimize the change of atmosphere over a period of time in all paths for infrared rays. In the conventional apparatus, this point is not taken into any consideration, so that a change of vapor, carbon dioxide gas, etc. in the optical path over a period of time sometimes causes noise in the high-sensitivity measurement of a microfine region of a sample.
As described above, in an infrared spectrum measuring apparatus, the chemical species (functional groups) of a material are identified. That is, since the infrared spectrum of a compound shows the infrared spectrum which is characteristic of the compound, it can be used for identification. However, since most of the objects of measurement are generally mixtures not single materials, the spectra obtained are complicated and difficult to explain. Furthermore, since identification is conventionally made only by an infrared spectrum, it is lacking in accuracy.
That is, the prior art aims only at measuring the infrared spectrum of a microfine portion, and the identification of the material from the spectrum obtained is insufficient and lacking in the accuracy of the identification of the chemical species.